Measure by weight: 4 ounces of water, 4 ounces of bread flour (between 2 3 and 3 4 of a cup in volume) and a pinch of active dry yeast; combine in a bowl, stirring thoroughly. Cover loosely with a few layers of cheesecloth, as the mixture needs good airflow and is likely to draw fruit flies. Let it sit at room temperature.

When the mixture is bubbly (in a warm room, this might take half a day), discard half of it and add another 1 2 cup of water and 3 4 cup of flour. Cover and let sit at room temperature for 1 day, then repeat the discard-half-and-fill step. Repeat this daily for 1 week.

While you are growing a culture of baking yeast, Hall says, the yeasts in your local environment get a chance to move in as well. "Mileage may vary," she says, because all starters are a little different, or they become so over time.

After four to seven days, the culture should have a sour and yeasty smell; a drop of it on the tongue will tingle. There might be some water liquid sitting on top of the culture that is yellowish or greenish-gray. Some people discard the liquid, but Hall mixes it in. (However, if the color is pink or orange, get rid of the liquid.)

At that point, transfer the starter to the refrigerator. After Hall measures out the amount called for in a recipe, she adds equal amounts of water and flour to the starter and lets it sit at room temperature for eight to 12 hours before returning it to the fridge.

She feeds her starter once a week whether or not any of it gets used. The longest she has let it go without feeding it is two weeks (while she was on vacation).

If a home baker wants just enough starter to make a single batch of bread and does not want to maintain a starter, Hall recommends creating a sponge of 7 ounces of water, 7 ounces of flour (between 11 4 and 11 3 cups) and a pinch of active dry yeast. Cover and let it sit overnight. Bake with all of it or refrigerate it for up to a day.

The sponge will not add the complex flavors of sourdough, she says, but it will make for good-tasting bread.